1. Field of the Invention
This invention relates to a device for detecting damage on rotators or rotary bodies such as for example ball bearings having rolling elements, and more particularly to such rotator damage detecting device in which the mechanical vibration or sound produced periodically due to damage on a rotator when it is rotated is converted into an electric signal so as to identify such damage on the rotator by utilizing the periodic characteristic of said electric signal.
2. Description of the Prior Art
If a rotator such as for example a ball bearing has a flaw in its surface, mechanical vibration may be produced by such flaw when the rotator is rotated, and such mechanical vibration causes noise or other unfavorable results. Such flaws may be produced in the course of manufacture of the rotator or may develop from a dent or flaking which results from fatigue of the rotator in use.
Recently, more and more high-degree precision of the rotators such as above-mentioned is requested in certain fields or their use, and in order to meet such request, high-degree techniques for check and evaluation of the products are necessitated.
Heretofore, quality check of for example the ball bearings has been practiced by rotating the inner race, outer race and balls of each bearing relative to each other and measuring oscillation produced during rotation of the bearings. In a certain type of conventional detecting device, there is used a vibration pick-up for converting mechanical oscillation of the bearing into an electric signal and the output signal is frequency-discriminated to sort out the defectives according to the frequency ranges. However, since the defectives result not only from such flaws but also from other causes such as mixing of alien matters into grease, it is impossible to detect the flaws alone by such frequency discrimination method, and hence generally additional work is necessitated for further classifying the defectives by their types for post-treatments, thus making it hardly attainable to rationalize the working process.
In still another known checking device, it is attempted to find out the flaws or other damage by detecting the impulsive oscillation which is produced when the bearing is damaged by using a vibration pick-up and measuring the peak values of the electric signal produced therefrom. There are known roughly two types of methods for measuring such peak values. In one of such methods, the maximum peak voltages are retained substantially and the highest peak value thereof is measured by keeping it static. According to another method, the value of the signal voltage close to the envelope is measured by a peak detection circuit adapted with a suitable discharge time constant.
These method, however, have the following defects. That is, in the case of the former method, since the peak values resulting from sudden impulsive vibration caused by external disturbance or from electric noise are also retained, it is sometimes found hard to distinguish between such peak values and the ones associated with damage on the bearing, while in the latter method, it may become impossible to follow up the impulse signal produced from damage when the discharge time constant is short, making it impossible to measure the correct peak values, and when the time constant is long, the same problem as in the case of the former method arises.